1. Field of the Invention
The present invention relates to a data processing apparatus which effectively performs data fetch and data output in a digital processor comprising a microprocessor or the like which performs control of operation of a copying machine.
2. Description of the Prior Art
In a digital processor of this type, adjustment of the gain and the difference (the latter to be referred to as an offset hereinafter) between the input value and the recognized value in analog to digital conversion is performed through adjustment of, for example, a variable resistor in an analog-to-digital converter (A/D converter) of the processor. If such adjustment with a variable resistor or the like is not performed, the A/D converter must have a high precision. Adjustment of the offset and gain by means of the A/D converter is performed through calibration of the input section of the A/D converter. Therefore, if a level shift circuit is incorporated in the stage preceding the A/D converter, not only the A/D converter but also the level shift circuit must be calibrated.
Adjustment of the gain of the analog input to the digital processor must be performed in accordance with the difference between the respective gains of the A/D converter, the multiplexer and so on which make up the digital processor. Such adjustment is cumbersome.
If an analog signal must be produced from a digital processor, the offset calibration (reference value setting) and gain adjustment must be performed at the output side.
Adjustment of the reference value and gain for obtaining the digital output from the digital processor is conventionally performed through adjustment of a variable resistor incorporated in a D/A converter of the processor. If such adjustment is not performed, the D/A converter must have a high precision. Adjustment of the reference value and gain by means of the D/A converter is performed by calibration at the output side of the D/A converter. Therefore, if a driver circuit or the like is incorporated at the stage next to the D/A converter, the adjustment must be performed for the driver circuit or the like as well as for the D/A converter.
In addition, the adjustment of the reference value and the gain of the digital output from the digital processor must be performed in accordance with the difference between the gains of the D/A converter, the multiplexer and so on.